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tokenizer.py
# Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license # Copyright (C) 2003-2017 Nominum, Inc. # # Permission to use, copy, modify, and distribute this software and its # documentation for any purpose with or without fee is hereby granted, # provided that the above copyright notice and this permission notice # appear in all copies. # # THE SOFTWARE IS PROVIDED "AS IS" AND NOMINUM DISCLAIMS ALL WARRANTIES # WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF # MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NOMINUM BE LIABLE FOR # ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES # WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN # ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT # OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. """Tokenize DNS zone file format""" import io import sys from typing import Any, List, Tuple import dns.exception import dns.name import dns.ttl _DELIMITERS = {" ", "\t", "\n", ";", "(", ")", '"'} _QUOTING_DELIMITERS = {'"'} EOF = 0 EOL = 1 WHITESPACE = 2 IDENTIFIER = 3 QUOTED_STRING = 4 COMMENT = 5 DELIMITER = 6 class UngetBufferFull(dns.exception.DNSException): """An attempt was made to unget a token when the unget buffer was full.""" class Token: """A DNS zone file format token. ttype: The token type value: The token value has_escape: Does the token value contain escapes? """ def __init__( self, ttype: int, value: Any = "", has_escape: bool = False, comment: str | None = None, ): """Initialize a token instance.""" self.ttype = ttype self.value = value self.has_escape = has_escape self.comment = comment def is_eof(self) -> bool: return self.ttype == EOF def is_eol(self) -> bool: return self.ttype == EOL def is_whitespace(self) -> bool: return self.ttype == WHITESPACE def is_identifier(self) -> bool: return self.ttype == IDENTIFIER def is_quoted_string(self) -> bool: return self.ttype == QUOTED_STRING def is_comment(self) -> bool: return self.ttype == COMMENT def is_delimiter(self) -> bool: # pragma: no cover (we don't return delimiters yet) return self.ttype == DELIMITER def is_eol_or_eof(self) -> bool: return self.ttype == EOL or self.ttype == EOF def __eq__(self, other): if not isinstance(other, Token): return False return self.ttype == other.ttype and self.value == other.value def __ne__(self, other): if not isinstance(other, Token): return True return self.ttype != other.ttype or self.value != other.value def __str__(self): return f'{self.ttype} "{self.value}"' def unescape(self) -> "Token": if not self.has_escape: return self unescaped = "" l = len(self.value) i = 0 while i < l: c = self.value[i] i += 1 if c == "\\": if i >= l: # pragma: no cover (can't happen via get()) raise dns.exception.UnexpectedEnd c = self.value[i] i += 1 if c.isdigit(): if i >= l: raise dns.exception.UnexpectedEnd c2 = self.value[i] i += 1 if i >= l: raise dns.exception.UnexpectedEnd c3 = self.value[i] i += 1 if not (c2.isdigit() and c3.isdigit()): raise dns.exception.SyntaxError codepoint = int(c) * 100 + int(c2) * 10 + int(c3) if codepoint > 255: raise dns.exception.SyntaxError c = chr(codepoint) unescaped += c return Token(self.ttype, unescaped) def unescape_to_bytes(self) -> "Token": # We used to use unescape() for TXT-like records, but this # caused problems as we'd process DNS escapes into Unicode code # points instead of byte values, and then a to_text() of the # processed data would not equal the original input. For # example, \226 in the TXT record would have a to_text() of # \195\162 because we applied UTF-8 encoding to Unicode code # point 226. # # We now apply escapes while converting directly to bytes, # avoiding this double encoding. # # This code also handles cases where the unicode input has # non-ASCII code-points in it by converting it to UTF-8. TXT # records aren't defined for Unicode, but this is the best we # can do to preserve meaning. For example, # # foo\u200bbar # # (where \u200b is Unicode code point 0x200b) will be treated # as if the input had been the UTF-8 encoding of that string, # namely: # # foo\226\128\139bar # unescaped = b"" l = len(self.value) i = 0 while i < l: c = self.value[i] i += 1 if c == "\\": if i >= l: # pragma: no cover (can't happen via get()) raise dns.exception.UnexpectedEnd c = self.value[i] i += 1 if c.isdigit(): if i >= l: raise dns.exception.UnexpectedEnd c2 = self.value[i] i += 1 if i >= l: raise dns.exception.UnexpectedEnd c3 = self.value[i] i += 1 if not (c2.isdigit() and c3.isdigit()): raise dns.exception.SyntaxError codepoint = int(c) * 100 + int(c2) * 10 + int(c3) if codepoint > 255: raise dns.exception.SyntaxError unescaped += b"%c" % (codepoint) else: # Note that as mentioned above, if c is a Unicode # code point outside of the ASCII range, then this # += is converting that code point to its UTF-8 # encoding and appending multiple bytes to # unescaped. unescaped += c.encode() else: unescaped += c.encode() return Token(self.ttype, bytes(unescaped)) class Tokenizer: """A DNS zone file format tokenizer. A token object is basically a (type, value) tuple. The valid types are EOF, EOL, WHITESPACE, IDENTIFIER, QUOTED_STRING, COMMENT, and DELIMITER. file: The file to tokenize ungotten_char: The most recently ungotten character, or None. ungotten_token: The most recently ungotten token, or None. multiline: The current multiline level. This value is increased by one every time a '(' delimiter is read, and decreased by one every time a ')' delimiter is read. quoting: This variable is true if the tokenizer is currently reading a quoted string. eof: This variable is true if the tokenizer has encountered EOF. delimiters: The current delimiter dictionary. line_number: The current line number filename: A filename that will be returned by the where() method. idna_codec: A dns.name.IDNACodec, specifies the IDNA encoder/decoder. If None, the default IDNA 2003 encoder/decoder is used. """ def __init__( self, f: Any = sys.stdin, filename: str | None = None, idna_codec: dns.name.IDNACodec | None = None, ): """Initialize a tokenizer instance. f: The file to tokenize. The default is sys.stdin. This parameter may also be a string, in which case the tokenizer will take its input from the contents of the string. filename: the name of the filename that the where() method will return. idna_codec: A dns.name.IDNACodec, specifies the IDNA encoder/decoder. If None, the default IDNA 2003 encoder/decoder is used. """ if isinstance(f, str): f = io.StringIO(f) if filename is None: filename = "<string>" elif isinstance(f, bytes): f = io.StringIO(f.decode()) if filename is None: filename = "<string>" else: if filename is None: if f is sys.stdin: filename = "<stdin>" else: filename = "<file>" self.file = f self.ungotten_char: str | None = None self.ungotten_token: Token | None = None self.multiline = 0 self.quoting = False self.eof = False self.delimiters = _DELIMITERS self.line_number = 1 assert filename is not None self.filename = filename if idna_codec is None: self.idna_codec: dns.name.IDNACodec = dns.name.IDNA_2003 else: self.idna_codec = idna_codec def _get_char(self) -> str: """Read a character from input.""" if self.ungotten_char is None: if self.eof: c = "" else: c = self.file.read(1) if c == "": self.eof = True elif c == "\n": self.line_number += 1 else: c = self.ungotten_char self.ungotten_char = None return c def where(self) -> Tuple[str, int]: """Return the current location in the input. Returns a (string, int) tuple. The first item is the filename of the input, the second is the current line number. """ return (self.filename, self.line_number) def _unget_char(self, c: str) -> None: """Unget a character. The unget buffer for characters is only one character large; it is an error to try to unget a character when the unget buffer is not empty. c: the character to unget raises UngetBufferFull: there is already an ungotten char """ if self.ungotten_char is not None: # this should never happen! raise UngetBufferFull # pragma: no cover self.ungotten_char = c def skip_whitespace(self) -> int: """Consume input until a non-whitespace character is encountered. The non-whitespace character is then ungotten, and the number of whitespace characters consumed is returned. If the tokenizer is in multiline mode, then newlines are whitespace. Returns the number of characters skipped. """ skipped = 0 while True: c = self._get_char() if c != " " and c != "\t": if (c != "\n") or not self.multiline: self._unget_char(c) return skipped skipped += 1 def get(self, want_leading: bool = False, want_comment: bool = False) -> Token: """Get the next token. want_leading: If True, return a WHITESPACE token if the first character read is whitespace. The default is False. want_comment: If True, return a COMMENT token if the first token read is a comment. The default is False. Raises dns.exception.UnexpectedEnd: input ended prematurely Raises dns.exception.SyntaxError: input was badly formed Returns a Token. """ if self.ungotten_token is not None: utoken = self.ungotten_token self.ungotten_token = None if utoken.is_whitespace(): if want_leading: return utoken elif utoken.is_comment(): if want_comment: return utoken else: return utoken skipped = self.skip_whitespace() if want_leading and skipped > 0: return Token(WHITESPACE, " ") token = "" ttype = IDENTIFIER has_escape = False while True: c = self._get_char() if c == "" or c in self.delimiters: if c == "" and self.quoting: raise dns.exception.UnexpectedEnd if token == "" and ttype != QUOTED_STRING: if c == "(": self.multiline += 1 self.skip_whitespace() continue elif c == ")": if self.multiline <= 0: raise dns.exception.SyntaxError self.multiline -= 1 self.skip_whitespace() continue elif c == '"': if not self.quoting: self.quoting = True self.delimiters = _QUOTING_DELIMITERS ttype = QUOTED_STRING continue else: self.quoting = False self.delimiters = _DELIMITERS self.skip_whitespace() continue elif c == "\n": return Token(EOL, "\n") elif c == ";": while 1: c = self._get_char() if c == "\n" or c == "": break token += c if want_comment: self._unget_char(c) return Token(COMMENT, token) elif c == "": if self.multiline: raise dns.exception.SyntaxError( "unbalanced parentheses" ) return Token(EOF, comment=token) elif self.multiline: self.skip_whitespace() token = "" continue else: return Token(EOL, "\n", comment=token) else: # This code exists in case we ever want a # delimiter to be returned. It never produces # a token currently. token = c ttype = DELIMITER else: self._unget_char(c) break elif self.quoting and c == "\n": raise dns.exception.SyntaxError("newline in quoted string") elif c == "\\": # # It's an escape. Put it and the next character into # the token; it will be checked later for goodness. # token += c has_escape = True c = self._get_char() if c == "" or (c == "\n" and not self.quoting): raise dns.exception.UnexpectedEnd token += c if token == "" and ttype != QUOTED_STRING: if self.multiline: raise dns.exception.SyntaxError("unbalanced parentheses") ttype = EOF return Token(ttype, token, has_escape) def unget(self, token: Token) -> None: """Unget a token. The unget buffer for tokens is only one token large; it is an error to try to unget a token when the unget buffer is not empty. token: the token to unget Raises UngetBufferFull: there is already an ungotten token """ if self.ungotten_token is not None: raise UngetBufferFull self.ungotten_token = token def next(self): """Return the next item in an iteration. Returns a Token. """ token = self.get() if token.is_eof(): raise StopIteration return token __next__ = next def __iter__(self): return self # Helpers def get_int(self, base: int = 10) -> int: """Read the next token and interpret it as an unsigned integer. Raises dns.exception.SyntaxError if not an unsigned integer. Returns an int. """ token = self.get().unescape() if not token.is_identifier(): raise dns.exception.SyntaxError("expecting an identifier") if not token.value.isdigit(): raise dns.exception.SyntaxError("expecting an integer") return int(token.value, base) def get_uint8(self) -> int: """Read the next token and interpret it as an 8-bit unsigned integer. Raises dns.exception.SyntaxError if not an 8-bit unsigned integer. Returns an int. """ value = self.get_int() if value < 0 or value > 255: raise dns.exception.SyntaxError(f"{value} is not an unsigned 8-bit integer") return value def get_uint16(self, base: int = 10) -> int: """Read the next token and interpret it as a 16-bit unsigned integer. Raises dns.exception.SyntaxError if not a 16-bit unsigned integer. Returns an int. """ value = self.get_int(base=base) if value < 0 or value > 65535: if base == 8: raise dns.exception.SyntaxError( f"{value:o} is not an octal unsigned 16-bit integer" ) else: raise dns.exception.SyntaxError( f"{value} is not an unsigned 16-bit integer" ) return value def get_uint32(self, base: int = 10) -> int: """Read the next token and interpret it as a 32-bit unsigned integer. Raises dns.exception.SyntaxError if not a 32-bit unsigned integer. Returns an int. """ value = self.get_int(base=base) if value < 0 or value > 4294967295: raise dns.exception.SyntaxError( f"{value} is not an unsigned 32-bit integer" ) return value def get_uint48(self, base: int = 10) -> int: """Read the next token and interpret it as a 48-bit unsigned integer. Raises dns.exception.SyntaxError if not a 48-bit unsigned integer. Returns an int. """ value = self.get_int(base=base) if value < 0 or value > 281474976710655: raise dns.exception.SyntaxError( f"{value} is not an unsigned 48-bit integer" ) return value def get_string(self, max_length: int | None = None) -> str: """Read the next token and interpret it as a string. Raises dns.exception.SyntaxError if not a string. Raises dns.exception.SyntaxError if token value length exceeds max_length (if specified). Returns a string. """ token = self.get().unescape() if not (token.is_identifier() or token.is_quoted_string()): raise dns.exception.SyntaxError("expecting a string") if max_length and len(token.value) > max_length: raise dns.exception.SyntaxError("string too long") return token.value def get_identifier(self) -> str: """Read the next token, which should be an identifier. Raises dns.exception.SyntaxError if not an identifier. Returns a string. """ token = self.get().unescape() if not token.is_identifier(): raise dns.exception.SyntaxError("expecting an identifier") return token.value def get_remaining(self, max_tokens: int | None = None) -> List[Token]: """Return the remaining tokens on the line, until an EOL or EOF is seen. max_tokens: If not None, stop after this number of tokens. Returns a list of tokens. """ tokens = [] while True: token = self.get() if token.is_eol_or_eof(): self.unget(token) break tokens.append(token) if len(tokens) == max_tokens: break return tokens def concatenate_remaining_identifiers(self, allow_empty: bool = False) -> str: """Read the remaining tokens on the line, which should be identifiers. Raises dns.exception.SyntaxError if there are no remaining tokens, unless `allow_empty=True` is given. Raises dns.exception.SyntaxError if a token is seen that is not an identifier. Returns a string containing a concatenation of the remaining identifiers. """ s = "" while True: token = self.get().unescape() if token.is_eol_or_eof(): self.unget(token) break if not token.is_identifier(): raise dns.exception.SyntaxError s += token.value if not (allow_empty or s): raise dns.exception.SyntaxError("expecting another identifier") return s def as_name( self, token: Token, origin: dns.name.Name | None = None, relativize: bool = False, relativize_to: dns.name.Name | None = None, ) -> dns.name.Name: """Try to interpret the token as a DNS name. Raises dns.exception.SyntaxError if not a name. Returns a dns.name.Name. """ if not token.is_identifier(): raise dns.exception.SyntaxError("expecting an identifier") name = dns.name.from_text(token.value, origin, self.idna_codec) return name.choose_relativity(relativize_to or origin, relativize) def get_name( self, origin: dns.name.Name | None = None, relativize: bool = False, relativize_to: dns.name.Name | None = None, ) -> dns.name.Name: """Read the next token and interpret it as a DNS name. Raises dns.exception.SyntaxError if not a name. Returns a dns.name.Name. """ token = self.get() return self.as_name(token, origin, relativize, relativize_to) def get_eol_as_token(self) -> Token: """Read the next token and raise an exception if it isn't EOL or EOF. Returns a string. """ token = self.get() if not token.is_eol_or_eof(): raise dns.exception.SyntaxError( f'expected EOL or EOF, got {token.ttype} "{token.value}"' ) return token def get_eol(self) -> str: return self.get_eol_as_token().value def get_ttl(self) -> int: """Read the next token and interpret it as a DNS TTL. Raises dns.exception.SyntaxError or dns.ttl.BadTTL if not an identifier or badly formed. Returns an int. """ token = self.get().unescape() if not token.is_identifier(): raise dns.exception.SyntaxError("expecting an identifier") return dns.ttl.from_text(token.value)
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